1. Technical Field
The present invention relates to a liquid ejecting apparatus such as an ink jet recording apparatus, in particular, relates to a liquid ejecting apparatus including a linear encoder used for recognizing a scanning position of a liquid ejecting head unit.
2. Related Art
A liquid ejecting apparatus includes a liquid ejecting head which can eject liquid in form of liquid droplets and ejects various liquids from the liquid ejecting head. As a representative example of the liquid ejecting apparatus, an image recording apparatus such as an ink jet recording apparatus (printer) which includes an ink jet recording head (hereinafter, referred to as recording head) and ejects ink in a liquid state in form of ink droplets through nozzles of the recording head to perform recording can be exemplified. In recent years, the liquid ejecting apparatus is not limited to the image recording apparatus and is applied to various manufacturing apparatuses such as a display manufacturing apparatus. Further, the above image recording apparatus ejects ink in a liquid state from the recording head and the display manufacturing apparatus ejects solutions of color materials of Red (R), Green (G), and Blue (B) from a color material ejecting head. Further, an electrode manufacturing apparatus ejects an electrode material in a liquid state from an electrode material ejecting head. A chip manufacturing apparatus ejects a solution of a bioorganic material from a bioorganic ejecting head.
There is a liquid ejecting apparatus which ejects liquid onto a landing target such as recording paper while moving (scanning) a liquid ejecting head. In such liquid ejecting apparatus, liquid droplets need to be landed onto the landing target (corresponding to recording paper in a printer, for example) with high accuracy. Therefore, a linear encoder which recognizes a scanning position of the liquid ejecting head is provided in the liquid ejecting apparatus. The linear encoder is constituted by a linear scale having scales marked at a constant interval in a lengthwise direction and a detector which reads the scale on the linear scale. Various detection systems such as a magnetic system and an optical system are employed for the linear encoder. Further, the linear scale is arranged over a scanning range of the liquid ejecting head in the liquid ejecting apparatus. For example, in a printer as one type of the liquid ejecting apparatus, an encoder pulse is generated from the detector of the above linear encoder with movement of the recording head and a timing signal PTS (print timing signal) is generated from the encoder pulse. Then, transfer of print data, generation of a driving signal, ejection of ink from the recording head, and the like are controlled in synchronization with the encoder PTS signal (for example, see, JP-A-2010-214608). If such control is performed, an actual position of the liquid ejecting head and a control position of the ejecting head can be made identical to each other with high accuracy, thereby enhancing accuracy of the landing position of liquid droplets.
There is a printer having the following configuration as an example of the above printer. That is, a plurality of recording heads which have nozzle rows on which a plurality of nozzles are arranged in rows and are arranged in a scanning direction and secured to a head securing member such as a sub carriage are configured as one head unit. In the printer employing such configuration, when materials of the above linear scale and head securing member are different from each other, linear expansion coefficients of them are also different from each other. Therefore, landing positions of liquid droplets on a recording medium are deviated between the recording heads secured to the head securing member in some case. The landing positions of liquid droplets are deviated because of difference between a change amount of a distance between nozzle rows on the recording heads and a deformation amount of the linear scale when a sub carriage is deformed due to change of an environmental temperature. As a result, there has arisen a risk that image quality of a recorded image or the like is deteriorated. In particular, as the number of liquid ejecting heads secured to the head securing member is larger and the head unit is longer in the main scanning direction, influence by the deviation of the landing positions based on the difference of the linear expansion coefficients tends to be larger. In order to prevent the above problem from occurring, it can be considered that the linear scale and the head securing member are formed with the same material. However, in such a case, freedom of selection of materials is restricted.
It is to be noted that the above problem occurs not only in the ink jet recording apparatus on which recording heads for ejecting ink are mounted but also in other liquid ejecting apparatuses. To be more specific, the above problem also occurs in other liquid ejecting apparatuses having a configuration in which a plurality of liquid ejecting heads are secured to a head securing member to form a liquid ejecting head unit and a position of the liquid ejecting head unit in a scanning direction is detected by a linear encoder.